In the past, resources of a data processing system have been allocated with the aid of appropriate hardware, logic devices and software. The allocation has been controlled from an operator's console. Such a system is described in an article entitled "DIPS 1 System Supervision and Control" appearing in the journal entitled "Review of the Electrical Communication Laboratories", Volume 21, Numbers 3-4, March-April, 1973. In the system described in this article, the data processing system is provided with a configuration that resolves the logic problems to each of the users. Connection states between different sub-units of the system are modified as a function of state switches at the operator's console, either by manipulating the switches directly or by initiating a special reconfiguration program in a memory of the system.
Another system for allocating resources of a data processing system is disclosed in U.S. Pat. No. 4,014,005, entitled "Configuration And Control Unit For A Hetergeneous Multisystem", directed to a configuration unit (CACV) for different types of processors associated with peripheral units of various input-output channels. The configuration unit is controlled from an operator's console and is situated at a central point of the data processing system, enabling the configuration unit to communicate directly with all elements of the system with the aid of cross bar channel multiplexers. The configuration unit disclosed in U.S. Pat. No. 4,014,005 does not adapt easily to a data processing system that is organized around a single bus containing address, data and control information primarily because the multiplexing units are a significant burden on the constitution of the system.
To resolve this problem, a purely logic solution is often used in systems organized around a single bus containing address, data and control signals. The logic solution involves establishing, for each user, a purely artificial system configuration that executes programs stored in the system memory unit. The artificial system configuration is due to logic of "the virtual machine monitor software". In this solution of the allocation problem, the configuration of the actual system frequently differs from that presented by the virtual or artificial system.
The user of the artificial or virtual system enables several users to perform functions on the same real system by using different operating systems. The virtual or artificial system, however, does not enable a user to know the configuration which is assigned to him. This is particularly disadvantageous because a user may be disrupted by an operating program of another user of the system without his knowledge. To overcome this disadvantage, programmers frequently use protective algorithms which are not satisfactory because they are very unwieldy and upset the processing speed of the system.
It is, accordingly, one of the objects of the present invention to provide a new and improved central sub-system of a data processing system divided into several independent sub-units.
Another object of the invention is to provide a purely hardware device for providing a user of a data processing system sub-unit an actual view of the portion of the system assigned to him.
Another object of the invention is to enable sub-units of a data processing system central sub-system to function in a configuration which is associated only with the sub-unit, thereby avoiding disturbances to other sub-units and enabling the different sub-units to be simultaneously activated.
By utilizing hardware, instead of software, to solve the allocation resources problem, greater flexibility is provided. A judicial distribution of the hardware in the data processing system permits isolation in an absolute manner of each sub-unit of the central subsystem, enabling the sub-units to respond to configuration needs of the various users.